Flux composition and method of soldering

ABSTRACT

A flux composition is provided, comprising, as an initial component: a fluxing agent represented by formula I: 
                         
wherein R 1 , R 2 , R 3  and R 4  are independently selected from a hydrogen, a substituted C 1-80  alkyl group, an unsubstituted C 1-80  alkyl group, a substituted C 7-80  arylalkyl group and an unsubstituted C 7-80  arylalkyl group; and wherein zero to three of R 1 , R 2 , R 3  and R 4  is(are) hydrogen. Also provided is a method of soldering an electrical contact using the flux composition.

The present invention relates to a flux composition comprising, as aninitial component a fluxing agent represented by formula I, wherein R¹,R², R³ and R⁴ are independently selected from hydrogen, a substitutedC₁₋₈₀ alkyl group, an unsubstituted C₁₋₈₀ alkyl group, a substitutedC₇₋₈₀ arylalkyl group and an unsubstituted C₇₋₈₀ arylalkyl group; andwherein zero to three of R¹, R², R³ and R⁴ is(are) hydrogen. The presentinvention further relates to a method of soldering an electricalcontact.

Soldering processes ranging from manual, hand soldering methods toautomated soldering methods. The use of flux materials in solderingprocesses, both manual and automated, is also well known. In fact, theuse of solder alone generally will not result in an acceptableelectrical interconnection. Flux materials serve multiple functions inthe soldering process. For example, flux materials operate to remove anyoxides that may have formed on the metallic contacts (e.g., solderregions, contact pads, contact pins, copper plated through holes); toenhance wetting of solder onto the metallic contacts.

Various methods have been employed to apply flux materials to thesurface of a metallic contact during the soldering process. In somemethods, flux materials containing solder are used. For example, suchcombined materials have been provided in the form of an annular shapedwire incorporating a core of flux material. As the solder melts uponheating, the flux material in the core is activated, fluxing thesurfaces to be interconnected by the molten solder. Solder pastes arealso known in which a flux material and a solder powder are compoundedto form a generally homogenous stable suspension of solder particles inthe paste.

One commercially significant application of an automated solderingmethod is the manufacture of semiconductor devices. That is, reflowsoldering processes are commonly used in the automated production ofsemiconductor devices, wherein a semiconductor chip is mounted on to aprinted circuit board (PCB). In some such automated production methods,a solder paste is applied to a printed circuit board using, for example,screen printing or stencil printing. The semiconductor chip is thenbrought into contact with the PCB and the solder paste is heated toreflow the solder in the paste, forming electrical interconnects betweenthe semiconductor chip and the PCB. The heating may be facilitated by,for example, exposure of the solder paste to infrared light or byheating in an oven. In some applications, the semiconductor chip/PCBassembly is further treated with an under fill material thatsubstantially fills the interstitial area between the semiconductor chipand the PCB, encapsulating the interconnects.

Given the demands for the mass production of electronic devicescontaining circuits of increasing complexity and miniaturization, rapid,automated soldering processes have emerged, such as, for example, thoseincorporating pick and dip processes. In such processes, a flux can beapplied to a plurality of electrical contacts on a semiconductor chip bydipping the electrical contact portion of the semiconductor chip into abath of flux. The flux coated electrical contacts on the semiconductorchip can then be brought into contact with a PCB comprisingcorresponding electrical contacts and solder balls. The solder balls maythen be heated to reflow interconnecting the semiconductor chip and thePCB. Alternatively, the pick and dip process can be employed with devicecomponents that have electrical contacts with preapplied solder. Inthese processes, the preapplied solder is dip coated with the fluxmaterial and then brought into contact with the corresponding electricalcontact(s) and heated to reflow, forming the electrical interconnects.Many electronic components fit into this latter process category in thatthey are manufactured with a sufficient amount of solder on board thecomponent to facilitate interconnection of the component with anotherelectrical component (e.g., a PCB).

In most instances, use of commercially available fluxes leaves ionicresidues on the soldered regions, which may undesirably lead tocorrosion of circuitry and to short circuits. Accordingly, additionalprocess steps are required to remove such residues after formation ofthe soldered interconnections. For semiconductor device manufacturingprocesses, the solder connections formed between the semiconductor chipand the PCB result in a relatively small gap between the semiconductorchip and the PCB (e.g., <4 mils). Hence, it is very difficult to remove(i.e., clean) ionic residues remaining on the soldered regions followingthe soldering process. Even in processes where the soldered regions areaccessible (hence, facilitating cleaning operations), cleaningoperations create environmental concerns involving the disposal of thewaste generated during the cleaning operations.

Some low residue, no clean fluxes having a low solid content arecommercially available. One flux composition asserted to substantiallyminimize or substantially eliminate flux residues when solderingelectronic components is disclosed in United States Patent ApplicationPublication No. 20100175790 to Duchesne et al. Duchesne et al. disclosea composition of matter comprising a flux, wherein said flux consistsessentially of a combination of: (a) a fluxing agent; and (b) a solvent;wherein said fluxing agent: (1) comprises a keto acid; or (2) comprisesan ester acid; or (3) comprises a mixture of said keto acid with saidester acid; and wherein said solvent comprises a mixture of a tackysolvent selected from polyhydric alcohols or mixtures thereof, and anon-tacky solvent selected from monohydric alcohols or mixtures thereof.

Notwithstanding, there remains a need for flux compositions that arenon-curing, facilitate reliable soldering connections and arecustomizable to facilitate compatibility with conventional epoxy basedunder fill materials.

The present invention provides a flux composition comprising, as aninitial component: a fluxing agent represented by formula I:

wherein R¹, R², R³ and R⁴ are independently selected from a hydrogen, asubstituted C₁₋₈₀ alkyl group, an unsubstituted C₁₋₈₀ alkyl group, asubstituted C₇₋₈₀ arylalkyl group and an unsubstituted C₇₋₈₀ arylalkylgroup; and wherein zero to three of R¹, R², R³ and R⁴ is(are) ahydrogen.

The present invention provides a method of applying solder to anelectrical contact, comprising: providing an electrical contact;providing an flux composition of the present invention; applying theflux composition to the electrical contact; providing a solder; meltingthe solder; and, displacing the flux composition applied to theelectrical contact with the molten solder; wherein the molten soldermakes physical contact with the electrical contact and bonds to theelectrical contact.

DETAILED DESCRIPTION

The flux composition of the present invention is designed to facilitatecompatibilization with various under fill compositions, such that, thesoldered surfaces preferably do not require cleaning before applicationof an under fill composition to form a finished electrical joint.

The term “no clean flux composition” as used herein and in the appendedclaims refers to flux compositions that exhibit a low, or no, fluxresidue activity with <0.5 wt % halide content (i.e., fluxes that arecategorized as an ORL1 or ORL0 under IPC J-STD-004B).

The flux composition of the present invention comprises (consistsessentially of), as an initial component: a fluxing agent represented byformula I. Preferably, the flux composition is a non-curing composition(i.e., wherein the flux composition is free of compounds having two ormore reactive functional groups per molecule capable of reacting undersoldering conditions to form inter molecular covalent bonds and whereinthe fluxing agent does not contain two or more reactive functionalgroups per molecule capable of reacting under soldering conditions toform inter molecular covalent bonds).

The fluxing agent used in the flux composition of the present inventionis according to formula I, wherein R¹, R², R³ and R⁴ are independentlyselected from hydrogen, a substituted C₁₋₈₀ alkyl group, anunsubstituted C₁₋₈₀ alkyl group, a substituted C₇₋₈₀ arylalkyl group andan unsubstituted C₇₋₈₀ arylalkyl group (preferably wherein R¹, R², R³and R⁴ are independently selected from a hydrogen, a substituted C₁₋₂₀alkyl group, an unsubstituted C₁₋₂₀ alkyl group, a substituted C₇₋₃₀arylalkyl group and an unsubstituted C₇₋₃₀ arylalkyl group); whereinzero to three of R¹, R², R³ and R⁴ is(are) hydrogen. Preferably, one tothree of R¹, R², R³ and R⁴ is(are) hydrogen. More preferably, two tothree of R¹, R², R³ and R⁴ are hydrogen. Still more preferably, two ofR¹, R², R³ and R⁴ are hydrogen. Most preferably, one of R¹ and R² ishydrogen and one of R³ and R⁴ is hydrogen. The R¹, R², R³ and R⁴ groupsof the fluxing agent according to formula I are preferably selected: toprovide the fluxing agent with desirable rheological properties for agiven application; optionally, to compatibilize the fluxing agent with agiven solvent package for delivery to the surface(s) to be soldered;and, optionally, to compatibilize the fluxing agent with a givenencapsulating composition (e.g., an epoxy resin) to be used postsoldering to form an encapsulated solder joint (e.g., for use inconventional flip chip under fill applications). Preferably, the R¹, R²,R³ and R⁴ groups of the fluxing agent according to formula I areselected to compatibilize the fluxing agent with a given encapsulatingcomposition such that the flux composition is a no clean fluxcomposition. Also, the R¹, R², R³ and R⁴ groups of the fluxing agentaccording to formula I are preferably selected to provide the fluxingagent with a boiling point temperature, determined by differentialscanning calorimetry of ≧250° C. (more preferably ≧300° C., mostpreferably ≧325° C.) and a percent weight loss of ≦10 wt % upon heatingto 250° C. determined by thermogravimetric analysis (TGA) using atemperature ramp of 10° C./min starting at 25° C.

More preferably, the fluxing agent used in the fluxing composition ofthe present invention is according to formula I; wherein R¹, R², R³ andR⁴ are independently selected from a hydrogen, a substituted C₁₋₈₀ alkylgroup, an unsubstituted C₁₋₈₀ alkyl group, a substituted C₇₋₈₀ arylalkylgroup and an unsubstituted C₇₋₈₀ arylalkyl group; wherein thesubstitutions in the substituted C₁₋₈₀ alkyl group and the substitutedC₇₋₈₀ arylalkyl group are selected from at least one of an —OH group, an—OR⁵ group, a —COR⁵— group, a —COR⁵ group, a —C(O)R⁵ group, a —CHOgroup, a —COOR⁵ group, an —OC(O)OR⁵ group, a —S(O)(O)R⁵ group, a —S(O)R⁵group, a —S(O)(O)NR⁵ ₂ group, an —OC(O)NR⁶ ₂ group, a —C(O)NR⁶ ₂ group,a —CN group, a —N(R⁶)— group and a —NO₂ group (preferably at least oneof an —OH group, an —OR⁵ group, a —COR⁵— group, a —COR⁵ group, a —C(O)R⁵group, a —CHO group, a —COOR⁵ group, an —OC(O)OR⁵ group, a —S(O)(O)R⁵group, a —S(O)R⁵ group, a —S(O)(O)NR⁵ ₂ group, an —OC(O)NR⁶ ₂ group, a—C(O)NR⁶ ₂ group, a —CN group and a —NO₂ group); wherein R⁵ is selectedfrom a C₁₋₂₈ alkyl group, a C₃₋₂₈ cycloalkyl group, a C₆₋₁₅ aryl group,a C₇₋₂₈ arylalkyl group and a C₇₋₂₈ alkylaryl group; wherein R⁶ isselected from a hydrogen, a C₁₋₂₈ alkyl group, a C₃₋₂₈ cycloalkyl group,a C₆₋₁₅ aryl group, a C₇₋₂₈ arylalkyl group and a C₇₋₂₈ alkylaryl group;and, wherein zero to three of R¹, R², R³ and R⁴ is(are) hydrogen. Thesubstituted C₁₋₈₀ alkyl group and the substituted C₇₋₈₀ arylalkyl groupcan contain combinations of substitutions. For example, the substitutedC₁₋₈₀ alkyl group and the substituted C₇₋₈₀ arylalkyl group can: containmore than one of the same type of substitution (e.g., two —OH groups);contain more than one type of substitution (e.g., an —OH group and a—COR⁵— group); contain more than one type of substitution with more thanone of the same type of substitution (e.g., two —OH groups and two—COR⁵— groups). Preferably, one to three of R¹, R², R³ and R⁴ is(are)hydrogen. More preferably, two to three of R¹, R², R³ and R⁴ arehydrogen. Still more preferably, two of R¹, R², R³ and R⁴ are hydrogen.Most preferably, one of R¹ and R² is hydrogen and one of R³ and R⁴ ishydrogen.

Still more preferably, the fluxing agent used in the fluxing compositionof the present invention is according to formula I; wherein R¹, R², R³and R⁴ are independently selected from a hydrogen, a substituted C₁₋₂₀alkyl group, an unsubstituted C₁₋₂₀ alkyl group, a substituted C₇₋₃₀arylalkyl group and an unsubstituted C₇₋₃₀ arylalkyl group; wherein thesubstitutions in the substituted C₁₋₂₀ alkyl group and the substitutedC₇₋₃₀ arylalkyl group are selected from at least one of an —OH group, an—OR⁷ group, a —COR⁷— group, a —COR⁷ group, a —C(O)R⁷ group, a —CHOgroup, a —COOR⁷ group, an —OC(O)OR⁷ group, a —S(O)(O)R⁷ group, a —S(O)R⁷group, a —S(O)(O)NR⁷ ₂ group, an —OC(O)NR⁸ ₂ group, a —C(O)NR⁸ ₂ group,a —CN group, a —N(R⁸)— group and a —NO₂ group (preferably at least oneof an —OH group, an —OR⁷ group, a —COR⁷— group, a —COR⁷ group, a —C(O)R⁷group, a —CHO group, a —COOR⁷ group, an —OC(O)OR⁷ group, a —S(O)(O)R⁷group, a —S(O)R⁷ group, a —S(O)(O)NR⁷ ₂ group, an —OC(O)NR⁸ ₂ group, a—C(O)NR⁸ ₂ group, a —CN group and a —NO₂ group); wherein R⁷ is selectedfrom a C₁₋₁₉ alkyl group, a C₃₋₁₉ cycloalkyl group, a C₆₋₁₅ aryl group,a C₇₋₁₉ arylalkyl group and a C₇₋₁₉ alkylaryl group; wherein R⁸ isselected from a hydrogen, a C₁₋₁₉ alkyl group, a C₃₋₁₀ cycloalkyl group,a C₆₋₁₅ aryl group, a C₇₋₁₀ arylalkyl group and a C₇₋₁₉ alkylaryl group;and, wherein zero to three of R¹, R², R³ and R⁴ is(are) hydrogen. Thesubstituted C₁₋₂₀ alkyl group and the substituted C₇₋₃₀ arylalkyl groupcan contain combinations of substitutions. For example, the substitutedC₁₋₂₀ alkyl group and the substituted C₇₋₃₀ arylalkyl group can: containmore than one of the same type of substitution (e.g., two —OH groups);contain more than one type of substitution (e.g., an —OH group and a—COR⁷— group); contain more than one type of substitution with more thanone of the same type of substitution (e.g., two —OH groups and two—COR⁷— groups). Preferably, one to three of R¹, R², R³ and R⁴ is(are)hydrogen. More preferably, two to three of R¹, R², R³ and R⁴ arehydrogen. Still more preferably, two of R¹, R², R³ and R⁴ are hydrogen.Most preferably, one of R¹ and R² is hydrogen and one of R³ and R⁴ ishydrogen.

Yet still more preferably, the fluxing agent used in the fluxingcomposition of the present invention is according to formula I; whereinR¹, R², R³ and R⁴ are independently selected from a hydrogen, a—CH₂CH(OH)R⁹ and a —CH₂CH(OH)CH₂—O—R⁹ group; wherein R⁹ is selected froma hydrogen, a C₁₋₂₈ alkyl group, a C₃₋₂₈ cycloalkyl group, a C₆₋₁₆ arylgroup, a C₇₋₂₈ arylalkyl group and a C₇₋₂₈ alkylaryl group (preferably,wherein R⁹ is selected from a C₅₋₁₀ alkyl group, a C₆₋₁₆ aryl group anda C₇₋₁₆ alkylaryl group; most preferably wherein R⁹ is selected from aC₈ alkyl group, a C₇ alkylaryl group and a naphthyl group); and whereinzero to three of R¹, R², R³ and R⁴ is(are) hydrogen. Preferably, one tothree of R¹, R², R³ and R⁴ is(are) hydrogen. More preferably, two tothree of R¹, R², R³ and R⁴ are hydrogen. Still more preferably, two ofR¹, R², R³ and R⁴ are hydrogen. Most preferably, one of R¹ and R² ishydrogen and one of R³ and R⁴ is hydrogen.

Preferably, the fluxing agent used in the flux composition of thepresent invention is according to formula I; wherein R¹ and R³ are ahydrogen; wherein R² and R⁴ are a —CH₂CH(OH)CH₂—O—R⁹ group; wherein R⁹is selected from a C₅₋₁₀ alkyl group, a C₇₋₁₆ alkylaryl group, anaphthyl group, a biphenyl group and a substituted C₁₂₋₁₆ biphenyl group(most preferably, wherein R⁹ is selected from a C₈ alkyl group, a C₇alkylaryl group and a naphthyl group). Preferably, the flux compositionis a no clean flux formulation.

Optionally, the fluxing agent used in the fluxing composition of thepresent invention is a dimer having a formula selected from formula IIa,IIb and IIc; wherein the dimer contains a first mer according to formulaI and a second mer according to formula I; wherein one of R¹, R², R³ andR⁴ of the first mer and one of R¹, R², R³ and R⁴ of the second mercoincide joining the first mer and the second mer.

An example of a dimer according to formula (IIa) is1-(2-ethylhexyloxy)-3-(4-(2-(3-(4-(2-(4-(3-(4-(2-(3-(heptan-3-yloxy)-2-hydroxypropylamino)propan-2-yl)-1-methylcyclohexylamino)-2-hydroxypropoxy)phenyl)propan-2-yl)phenoxy)-2-hydroxypropylamino)propan-2-yl)-1-methylcyclohexylamino)propan-2-ol,as follows:

The flux composition of the present invention optionally furthercomprises a solvent. Solvent is optionally included in the fluxcomposition of the present invention to facilitate delivery of thefluxing agent to the surface, or surfaces, to be soldered. Preferably,the flux composition contains 8 to 95 wt % solvent. Solvent used in theflux composition of the present invention is preferably an organicsolvent selected from hydrocarbons (e.g., dodecane, tetradecane);aromatic hydrocarbons (e.g., benzene, toluene, xylene, trimethylbenzene,butyl benzoate, dodecylbenzene); ketones (e.g., methyl ethyl ketone,methyl isobutyl ketone, cyclohexanone); ethers (e.g., tetrahydrofuran,1,4-dioxaneandtetrahydrofuran, 1,3-dioxalane, diprolylene glycoldimethyl ether); alcohols (e.g., 2-methoxy-ethanol, 2-butoxyethanol,methanol, ethanol, isopropanol, α-terpineol, benzyl alcohol,2-hexyldecanol,); esters (e.g., ethyl acetate, ethyl lactate, butylacetate, diethyl adipate, diethyl phthalate, diethylene glycol monobutylacetate, propylene glycol monomethyl ether acetate, ethyl lactate,methyl 2-hydroxyisobutyrate, propylene glycol monomethyl ether acetate);and, amides (e.g., N-methylpyrrolidone, N,N-dimethylformamide andN,N-dimethylacetamide); glycol derivatives (e.g., cellosolve, butylcellosolve); glycols (e.g., ethylene glycol; diethylene glycol;dipropylene glycol; triethylene glycol; hexylene glycol;1,5-pentanediol); glycol ethers (e.g., propylene glycol monomethylether, methyl carbitol, butyl carbitol); and petroleum solvents (e.g.,petroleum ether, naptha). More preferably, the solvent used in the fluxcomposition of the present invention is an organic solvent selected frommethyl ethyl ketone; 2-propanol; propylene glycol monomethyl ether;propylene glycol monomethyl ether acetate; ethyl lactate and methyl2-hydroxy isobutyrate. Most preferably, the solvent used in the fluxcomposition of the present invention is propylene glycol monomethylether.

The flux composition of the present invention optionally furthercomprises a thickening agent. Preferably, the flux composition contains0 to 30 wt % thickening agent. Thickening agent used in the fluxcomposition of the present invention can be selected from non-curingresin materials (i.e., <2 reactive functional groups per molecule), suchas, for example, a non-curing novolac resin.

The flux composition of the present invention optionally furthercomprises a thixotropic agent. Preferably, the flux composition contains1 to 30 wt % thixotropic agent. Thixotropic agent used in the fluxcomposition of the present invention can be selected from fatty acidamides (e.g., stearamide, hydroxystearic acid bisamide); fatty acidesters (e.g., castor wax, beeswax, carnauba wax); organic thixotropicagents (e.g., polyethylene glycol, polyethylene oxide, methyl cellulose,ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose,diglycerine monooleate, deglycerine laurate, decaglycerine oleate,diglycerine monolaurate, sorbitan laurate); inorganic thixotropic agents(e.g., silica powders, kaolin powders). Preferably, the thixotropicagent used is selected from a polyethylene glycol and a fatty acidamide.

The flux composition of the present invention optionally furthercomprise an inorganic filler. Inorganic fillers can be selected fromalumina, aluminum hydroxide, aluminosilicate, cordierite, lithiumaluminum silicate, magnesium aluminate, magnesium hydroxide, clay, talc,antimony trioxide, antimony pentoxide, zinc oxide, colloidal silica,fused silica, glass powder, quartz powder and glass microspheres.

The flux composition of the present invention optionally furthercomprises an antioxidant. Preferably, the flux composition of thepresent invention contains 0.01 to 30 wt % antioxidant.

The flux composition of the present invention optionally furthercomprises an additive selected from matting agents, coloring agents,defoaming agents, dispersion stabilizers, chelating agents,thermoplastic particles, UV impermeable agents, flame retardants,leveling agents, adhesion promoters and reducing agents.

The flux composition of the present invention preferably comprises(consists essentially of), as an initial component: 3.99 to 100 wt % ofa fluxing agent represented by formula I. Preferably, the fluxcomposition of the present invention comprises (consists essentiallyof), as initial components: 3.99 to 100 wt % of a fluxing agentrepresented by formula I, 0 to 95 wt % (more preferably 8 to 95 wt %) ofa solvent, 0 to 30 wt % thickening agent, 0 to 30 wt % (more preferably1 to 30 wt %) of a thixotropic agent, and 0 to 30 wt % (more preferably0.01 to 30 wt %) of an antioxidant.

The flux composition of the present invention can be used in, forexample, the production of electronic components, electronic modules andprinted circuit boards. The flux composition can be applied to thesurface(s) to be soldered by any conventional technique including, forexample, liquid spray techniques, liquid foaming techniques, pick anddip techniques and wave techniques or any other conventional techniquecapable of dispensing a liquid or semisolid onto a silicon die orsubstrate.

The flux composition of the present invention optionally furthercomprises a solder powder; wherein the flux composition is a solderpaste. Preferably, the solder powder is an alloy selected from Sn/Pb,Sn/Ag, Sn/Ag/Cu, Sn/Cu, Sn/Zn, Sn/Zn/Bi, Sn/Zn/Bi/In, Sn/Bi and Sn/In(preferably wherein the solder powder is an alloy selected from 63 wt %Sn/37 wt % Pb; 96.5 wt % Sn/3.5 wt % Ag; 96 wt % Sn/3.5 wt % Ag/0.5 wt %Cu; 96.4 wt % Sn/2.9 wt % Ag/0.5 wt % Cu; 96.5 wt % Sn/3 wt % Ag/0.5 wt% Cu; 42 wt % Sn/58 wt % Bi; 99.3 wt % Sn/0.7 wt % Cu; 91 wt % Sn/9 wt %Zn and 89 wt % Sn/8 wt % Zn/3 wt % Bi).

The solder paste preferably comprises: 1 to 50 wt % (more preferably 5to 30 wt %, most preferably 5 to 15 wt %) of a fluxing agent of thepresent invention and 50 to 99 wt % of a solder powder. The solder pastecan be compounded by conventional techniques, for example, by kneadingand mixing the solder powder with the fluxing agent using conventionalequipment for such operations.

The solder paste can be used in, for example, the production ofelectronic components, electronic modules and printed circuit boards.The solder paste can be applied to the surface(s) to be soldered by anyconventional technique including, for example, printing the solder pastethrough a conventional solder mask using a solder printer or screenprinter.

The fluxing agent used in the flux composition of the present inventioncan be prepared using conventional synthesis techniques well known tothose of ordinary skill in the art.

The method of applying solder to an electrical contact of the presentinvention comprises: providing an electrical contact; providing an fluxcomposition of the present invention; applying the flux composition tothe electrical contact; providing a solder; melting the solder; and,displacing the flux composition applied to the electrical contact withthe molten solder; wherein the molten solder makes physical contact withthe electrical contact and bonds to the electrical contact. In themethod, the molten solder desirably comes into intimate contact with theelectrical contact to facilitate formation of a metallic bond betweenthe solder material and the electrical contact, providing a goodmechanical and electrical bond between the solder and the electricalcontact. Any conventional soldering technique can be used in the methodof the present invention. For example, a soldering bit or iron can beused to heat the electrical contact and the solder to a temperatureabove the melting point temperature for the solder. A soldering bath canbe used, wherein solder in a liquid state is transferred to theelectrical contact through immersion of the electrical contact into themolten solder. Conventional wave soldering techniques can beimplemented. Also, reflow soldering techniques can also be used, whereinsolder previously deposited onto a second electrical contact is broughtinto proximity with the first electrical contact and heated to atemperature above the melting point temperature of the solder, whereinthe solder melts and reflows, coming into contact with both the firstelectrical contact and the second electrical contact, forming anelectrical contact between the first electrical contact and the secondelectrical contact.

The method of applying solder to an electrical contact of the presentinvention can optionally be part of a flip chip soldering process,wherein a semiconductor chip is mounted onto a printed circuit board,wherein the semiconductor chip comprises a plurality of first electricalcontacts and wherein the printed circuit board comprises a plurality ofsecond electrical contacts. In such flip chip method, the fluxcomposition of present invention is applied to either one, or both, ofthe plurality of first electrical contacts and the plurality of secondelectrical contacts to facilitate solder bonding of the plurality offirst electrical contacts to the plurality of second electrical contactsto form electrical interconnects. Preferably, the flip chip solderprocess further comprises an under fill step wherein a thermosettingresin is provided to encapsulate the electrical interconnects. Mostpreferably, the thermosetting resin is an epoxy resin.

Some embodiments of the present invention will now be described indetail in the following Examples.

Examples 1-5 Synthesis of Fluxing Agent

The fluxing agents identified in TABLE 1 were prepared from thematerials identified in TABLE 1 using the following procedure.Specifically, into a reaction vessel with a stir bar, (0.1 mol) menthanediamine (available from The Dow Chemical Company as Primene™ MD) wasadded. The reaction vessel was then placed on a hotplate with magneticstirring capability. The reaction vessel was then inerted with nitrogenand (0.2 mol) Reagent A identified in TABLE 1 was then added to thereaction vessel at ambient temperature, with stirring. The set pointtemperature on the hot plate was then raised to 75° C. and the contentsof the reaction vessel were allowed to continue stirring for two (2)hours. The set point temperature of the hot plate was then raised to140° C. and the contents of the reaction vessel were allowed to continuestirring for two (2) more hours. The set point temperature of the hotplate was then reduced to 80° C. and a vacuum was pulled on the reactionvessel, reducing the pressure in the vessel to 30 mm Hg. The contents ofthe reaction vessel were allowed to continue stirring under theseconditions for another two (2) hours to provide the product fluxingagent as identified in TABLE 1. The boiling point temperature of theproduct fluxing agents for Examples 1-3 were then measured bydifferential scanning calorimetry (DSC) using a ramp of 10° C./min. from25° C. to 500° C. The measured boiling point temperature (BPT) for theproduct fluxing agent for Examples 1-3 is provided in TABLE 1. Also, thepercent weight loss from the product fluxing agent for Examples 1-3 uponheating to 250° C. was measured by thermogravimetric analysis (TGA)using a temperature ramp of 10° C./min starting at 25° C. The measuredweight loss (WL) for the product fluxing agent for Examples 1-3 isprovided in TABLE 1.

TABLE 1 Ex. Reagent A Fluxing Agent 1 2-ethylhexyl glycidyl ether

BPT by DSC ≧ 325° C. WL by TGA = 9 wt % (@ 250° C.) 2 cresyl glycidylether

BPT by DSC ≧ 325° C. WL by TGA = 8 wt % (@ 250° C.) 3 1-naphthylglycidyl ether

BPT by DSC ≧ 325° C. WL by TGA = 8 wt % (@ 250° C.) 4 alkyl C₁₂₋₁₄glycidyl ether

5 p-t-butylphenyl glycidyl ether

Example 6 Synthesis of a Dimeric Fluxing Agent

A dimeric fluxing agent was prepared using the following procedure. Intoa reaction vessel with a stir bar, (34 g) of menthane diamine (availablefrom The Dow Chemical Company as Primene™) and (37.4 g) of a liquidreaction product of epichlorohydrin and bisphenol A (available from TheDow Chemical Company as D.E.R.™ 331™) were added. The reaction vesselwas then placed on a hotplate with magnetic stirring capability. Thecontents of the reaction vessel were left to stir at room temperatureovernight, turning into a solid. Then (37.2 g) of 2-ethylhexyl glycidylether (available from Momentive Performance Materials) was charged tothe reaction vessel. The reaction vessel was then heated up to 150° C.with a one hour ramp from room temperature and then held at 150° C. forthree hours. The contents of the reaction vessel were then allowed tocool to room temperature to provide a dimeric fluxing agent product.

Example 7 Synthesis of a Dimeric Fluxing Agent

Another dimeric fluxing agent was prepared using the followingprocedure. Into a reaction vessel with a stir bar, (34 g) of menthanediamine (available from The Dow Chemical Company as Primene™) and (37.4g) a liquid epoxy resin reaction product of epichlorohydrin andbisphenol A (available from The Dow Chemical Company as D.E.R.™ 331™)were added. The reaction vessel was then placed on a hotplate withmagnetic stirring capability. The contents of the reaction vessel wereleft to stir at room temperature overnight, turning into a solid. Then(40.0 g) of 1-naphthyl glycidyl ether (available from MomentivePerformance Materials) was charged to the reaction vessel. The reactionvessel was then heated up to 75° C. and held at that temperature for onehour. The reaction vessel was then further heated to 150° C. with a onehour ramp from 75° C. and then held at 150° C. for three hours. Thecontents of the reaction vessel were then allowed to cool to roomtemperature to provide a dimeric fluxing agent product.

Examples 8-14 Preparation of Flux Composition

The fluxing agent prepared according to each one of Examples 1-7 wasindividually combined with propylene glycol methyl ether acetate(available from The Dow Chemical Company as electronic grade solvent) ata 1:1 weight ratio to form the flux compositions of Examples 8-14,respectively.

Example 15 Evaluation of Fluxing Capability

The fluxing capability of each one of the flux compositions preparedaccording to Examples 8-14 was evaluated and compared with ahydroxystearic acid reference material using the following procedure. Ineach evaluation, a copper coupon was used as an electrical contact to besoldered. The surface to be soldered on each of the copper coupons waspretreated by: (1) first polishing with fine sand paper (600 grit), (2)then cleaning with a 5% ammonium persulfate solution, (3) then rinsingwith deionized water, (4) then dipping in a 1% benzotriazole solutionfor 30 seconds, and (5) then blow drying with nitrogen. Followingpretreatment of the copper coupons, a small drop of each one the fluxcompositions was individually dispensed onto the surface to be solderedof one of the copper coupons. Four 0.381 mm diameter balls of alead-free solder (95.5 wt % Sn/4.0 wt % Ag/0.5 wt % Cu) were placed intothe drop of flux composition on each of the copper coupons. The meltingrange of the lead-free solder used is 217 to 221° C. The copper couponswere then placed on a hotplate that was preheated to 145° C. and heldthere for two (2) minutes. The copper coupons were then placed onanother hotplate preheated to 260° C. and held there until the solderreached reflow conditions (45 sec. to 3 min. depending on the fluxcomposition present). The copper coupons were then removed from the heatand evaluated by (a) the extent of fusion and coalescence of theoriginally placed four solder balls, (b) the size of the resultingcoalesced solder to assess the flow and spread and (c) the bonding ofthe solder to the surface of the copper coupon. A scale of 0 to 4 wasused to describe the fluxing capability of the flux compositions and thehydroxystearic acid reference material, as follows:

-   -   0=no fusion between solder drops and no solder bonding to copper        coupon;    -   1,2=partial to complete fusion between solder drops, but no        solder bonding to copper coupon;    -   3=complete fusion between solder drops, but minimal solder        spread and flow;    -   4=complete fusion between solder drops, good solder spread and        flow over surface of copper coupon and solder bonding to the        copper coupon.        The result of the evaluation of each of the flux compositions is        provided in TABLE 2.

TABLE 2 Flux Composition Evaluation Result Example 8 4 Example 9 4Example 10 4 Example 11 4 Example 12 4 Example 13 4 Example 14 4Reference material 4 (hydroxystearic acid)

1. A flux composition comprising, as an initial component: a fluxingagent represented by formula I:

wherein R¹, R², R³ and R⁴ are independently selected from a hydrogen, asubstituted C₁₋₈₀ alkyl group, an unsubstituted C₁₋₈₀ alkyl group, asubstituted C₇₋₈₀ arylalkyl group and an unsubstituted C₇₋₈₀ arylalkylgroup; and wherein zero to three of R¹, R², R³ and R⁴ is(are) hydrogen.2. The flux composition of claim 1, wherein the substitutions in thesubstituted C₁₋₈₀ alkyl group and the substituted C₇₋₈₀ arylalkyl groupare selected from at least one of an —OH group, an —OR⁵ group, a —COR⁵—group, a —C(O)R⁵ group, a —COR⁵ group, a —CHO, a —COOR⁵ group, an—OC(O)OR⁵ group, a —S(O)(O)R⁵ group, a —S(O)R⁵ group, a —S(O)(O)NR⁵ ₂group, an —OC(O)NR⁶ ₂ group, a —C(O)NR⁶ ₂ group, a —CN group, a —N(R⁶)—group and a —NO₂ group; wherein R⁵ is selected from a C₁₋₂₈ alkyl group,a C₃₋₂₈ cycloalkyl group, a C₆₋₁₅ aryl group, a C₇₋₂₈ arylalkyl groupand a C₇₋₂₈ alkylaryl group; and, wherein R⁶ is selected from ahydrogen, a C₁₋₂₈ alkyl group, a C₃₋₂₈ cycloalkyl group, a C₆₋₁₅ arylgroup, a C₇₋₂₈ arylalkyl group and a C₇₋₂₈ alkylaryl group.
 3. The fluxcomposition of claim 1, wherein R¹, R², R³ and R⁴ are independentlyselected from a hydrogen, a —CH₂CH(OH)R⁹ and a —CH₂CH(OH)CH₂—O—R⁹ group;wherein R⁹ is selected from a hydrogen, a C₁₋₂₈ alkyl group, a C₃₋₂₈cycloalkyl group, a C₆₋₁₅ aryl group, a C₇₋₂₈ arylalkyl group and aC₇₋₂₈ alkylaryl group.
 4. The flux composition of claim 1, wherein oneto three of R¹, R², R³ and R⁴ is(are) hydrogen.
 5. The flux compositionof claim 1, further comprising a solvent, wherein the solvent is anorganic solvent selected from hydrocarbons, aromatic hydrocarbons,ketones, ethers, alcohols, esters, amides, glycols, glycol ethers,glycol derivatives and petroleum solvents.
 6. The flux composition ofclaim 1, further comprising at least one of: an inorganic filler; athixotropic agent; and an antioxidant.
 7. The flux composition of claim1, further comprising: an additive selected from matting agents,coloring agents, defoaming agents, dispersion stabilizers, chelatingagents, thermoplastic particles, UV impermeable agents, flameretardants, leveling agents, adhesion promoters and reducing agents. 8.The flux composition of claim 1, further comprising, as initialcomponents: 0 to 95 wt % of a solvent, 0 to 30 wt % of a thickeningagent, 0 to 30 wt % of a thixotropic agent, and 0 to 30 wt % of anantioxidant.
 9. The flux composition of claim 1, further comprising asolder powder.
 10. A method of applying solder to an electrical contact,comprising: providing an electrical contact; providing an fluxcomposition according to claim 1; applying the flux composition to theelectrical contact; providing a solder; melting the solder; and,displacing the flux composition applied to the electrical contact withthe molten solder; wherein the molten solder makes physical contact withthe electrical contact and bonds to the electrical contact.